Whenever a vehicle slows or brakes, energy is released. In current combustion engine vehicle designs the energy is not used, yet Tunestål’s new research shows that it is fully possible to save it for later use in the form of compressed air. Then it can provide extra power to the engine when the vehicle is started and save fuel by avoiding idle operation when the car is at a standstill.

The Lund team is in full research mode with experiments on working engines providing hard data output. Sasa Trajkovic, a doctoral student in Combustion Engines at Lund University who recently defended a thesis on the subject said, “This is the first time anyone has done experiments in an actual engine. The research so far has only been theoretical. In addition, we have used data that means we get credible driving cycle results, for example data from the driving patterns of buses in New York.”

The idea of air hybrids first came out from Ford in the 1990s, but the American car company quickly shelved the plans because it lacked the necessary technology to move forward with the project. Today, research on air hybrids is conducted at ETH in Switzerland, Orléans in France as well as and Lund University in Sweden

The idea is being called air hybrids, or pneumatic hybrids and are not yet in production. For now the savings is only available for electric vehicles and electric hybrid vehicles already making use of the brake energy to power a generator that recharges the batteries.

Using air has a massive market – most all stop and go engine powered vehicles could make use of compressed air system. The step to commercialization does not have to be a large one. Tunestål said, “The technology is fully realistic. I was recently contacted by a vehicle manufacturer in India which wanted to start making air hybrids.”

The ideal use example is stop and go work in urban environments. Trajkovic said, “My simulations show that buses in cities could reduce their fuel consumption by 60 per cent.” Now that’s a huge cut, something to whip the attention around of every bus operator world wide.

Even half right the numbers are a skinflint number crunchers dream come true.

Trajkovic has calculated that 48 per cent of the brake energy, which is compressed and saved in a small air tank connected to the engine, could be reused later. This means that the degree of reuse for air hybrids could match that of today’s electric hybrids. The engine does not require any expensive materials and is therefore cheap to manufacture. What is more, it takes up much less space than an electric hybrid engine. The method works with gasoline, natural gas and diesel. It would work on hydrogen or any biofuel as well.

Air Hybrid 1st Engine and Valve Kit at Lund. Click image for more info.

As the idea sits today the Lund research team has worked with the Swedish company Cargine, who supplies valve control systems. One company that intends to invest in engines with air hybrid technology is the American Scuderi, but their test results so far have been from simulations, not from experiments.

The researcher team at Lunds next step is converting their research results from a single cylinder to a complete, multi-cylinder engine. They would thus be able to move the concept one step closer to a real vehicle.

“During pneumatic hybrid operation the engine can be used as a 2-stroke compressor for generation of compressed air during vehicle deceleration (compressor mode) and during vehicle acceleration the engine can be operated as an air-motor driven by the previously stored pressurized air (air-motor mode). The compressed air is stored in a pressure tank connected to one of the inlet ports. One of the engine inlet valves has been modified to work as a tank valve in order to control the pressurized air flow to and from the pressure tank.

In order to switch between different modes of engine operation there is a need for a fully variable valve actuation (FVVA) system. The engines used in this study are equipped with pneumatic valve actuators that use compressed air in order to drive the valves and the motion of the valves is controlled by a combination of electronics and hydraulics.”